Electron tube apparatus



May 31, 1960 B, NELSON 2,939,036

ELECTRON TUBE APPARATUS Filed Nov. 14, 1955 3 Sheets-Sheet 1 INVENTORB01420 B. NELSON May 31, 1960 R B NELSON 2,939,036

ELECTRON TUBE APPARATUS Filed Nov. 14, 1955 3 Sheets-Sheet 2 /L INvENTaQ Z2 66 Elam/e0 5 Nil SON 3 Sheets-Sheet 3 INVENTOB y 31, 1960 R.B. NELSON ELECTRON TUBE APPARATUS Filed Nov. 14, 1955 TU VE'R P05/ 770FIE! l [3 19/0/4120 5. NELSON 8 I VL 6 T.

United States Patent 2,939,036 ELECTRON TUBE APPARATUS Richard B.Nelson, Los Altos, Calif., assignor to Varian Associates, San Carlos,Califi, a corporation of California Filed Nov. 14, 1955, Ser. No.546,624

Claims. (31. 3155.'47)

This invention relates in general to electron tube apparatus and morespecifically to a novel improved electron tube apparatus of the velocitymodulation type employing cavity resonator devices as, for example, highpower klystron tubes utilized in systems employed in radar, linearaccelerators, navigation beacons, microwave transmission, etc.

The life of a high power tube, heretofore, has been seriously limited bythe unreliability of output windows. Failure of the output windownormally causes a leak allowing the vacuum within the tube to go up toatmospheric pressure thereby rendering the tube inoperative andpermanently damaging the cathode necessitating its replacement. Also,the major cause of a tube falling below specification after its normalexpected life in operation is the exhaustion of its cathode. It has beenfound that many tubes may be returned to active use by merely replacingthe cathode and, therefore, a practical manner of easily removing andreplacing the cathode sections of such high power tubes has been sought.

High power multi-cavity amplifiers have been heretofore built having theindividual cavities tunable but thus far the cavities have beenseparately tuned, that is, tuned with separate tuning controls. Thisrequirement of being separately tuned has been due to the lack of asuitable tuning device possessing a linear frequency versus positioncharacteristic which could be gauged together. The present inventionprovides such a linear tuner and effectively gangs the tuners wherebythe multi-cavity tube may be tuned with a single control.

It is, therefore, the principal object of the present invention toprovide a novel high-power, high-gain electron tube apparatus which isrelatively compact in construction and which offers gang tuning, longlife, easy maintenance and electrical stability.

Another feature of the present invention is a novel impedancetransformer in cooperation with the output cavity resonator whereby themagnetic focusing coil may be made to extend up to and around the outputcavity thereby substantially reducing beam interception in the immediatevicinity of the output cavity resonator.

Another feature of the present invention is a novel tuning plungerhaving the desirable linear frequency versus position characteristicnecessary for gang tuning.

Another feature of the present invention is a novel shield for thetuning plunger cooperating with the tuning 2 tube apparatus of thisinvention shown partly in section, the top portion of the tube beingoffset to the right in this view andthe well-known focusing magnet andcathode structure of this tube apparatus being shown only fragmentarily,

Fig. 2 is an enlarged elevational view of a portion of the structure ofFig. 1 taken along line 2-2 looking in the direction of the arrows,

Fig. 3 is an enlarged fragmentary cross sectional view of a portion ofthe structure of Fig. 2 taken along the line 3-3 in the direction of thearrows,

Fig. 4 is an enlarged cross sectional view of a portion of the structureof Fig. l-taken along line 44 in the direction of the arrows,

Fig. 5 is a longitudinal cross sectional view of the structure of Fig. 4taken along line 5--5 in the direction of the arrows,

Fig. 6 is a transverse cross sectional view of a portion of thestructure of Fig. 5 taken along line 6-6 in the direction of the arrowsshowing electric and magneticlines,

Fig. 6A is a partial view of a structure similar to Fig. 6 having thetuning plunger fully extended,

Fig. 7 is an enlarged transverse section view of a portion of thestructure of Fig. 1 taken along line '7--7 in the direction of thearrows,

Fig. 8 is a longitudinal cross sectional view of a portion of thestructure of Fig. 7 taken along line 8-8 in the direction of the arrows,

Fig. 9 is an enlarged longitudinal part cross sectional view of aportion of the output cavity resonator structure of Fig. 1 including aportion of the tuning rod, and

Fig. 10 is a graph of frequency versus tuner position characteristicsfor a plurality of cavity resonators.

The construction of the novel tube apparatus will now be described withreference to the drawings followed by a description of its operation.

Shown at the bottom of the depicted structure in Fig. l is a partialview of a cathode assembly 1. At the other end of the structure is acollector assembly 2 and interposed between the cathode assembly 1 andthe collector assembly 2 is a radio frequency section 3. Surrounding theradio frequency section is a magnetic beam confining and focusingsolenoid 4.

The cathode assembly 1 contains an electron emissive element or cathode5 which in use provides a ready source of electrons. A positivepotential with respect to the cathode 5 is applied to an apertured anode6 (Figs. 1 and 5). The electric field thus established between thecathode 5 and anode 6 accelerates the electrons to a high velocity anddraws them through the apertured anode 6 toward the collector 2.

Successively arranged between the cathode 5 and collector 2 in the RP.section 3 are a plurality of cavity plunger to provide the desiredlinear tuning characterisresonators, input resonator 7, first bunchercavity 8, second buncher cavity 9 and output cavity 11. Mutually spacedapart drift tube sections 12 interconnect the cavity resonators andprovide interaction spaces or gaps within the respective cavityresonators. A signal-input coaxial line 13 is coupled into the inputcavity 7 by coaxial loop 14 (Fig. 5).

The output cavity resonator 11 is coupled to the load through an outputhis 15, an output waveguide 16 which incorporates a waveguide impedancetransformer 17, and output window 18.

The conventional three step binomial impedance transformer 17 has beendisposed outwardly of the output iris 15 thereby allowing a shallow highadmittance section of output waveguide 16 to be employed in theimmediate vicinity of the output cavity 11. The shallow sect-ion ofwaveguide 16 is then brought away from the output iris 15 parallel tothe longitudinal axis of the tube apparatus whereby the R.'F. sectiondiameter is kept to a minimum in the vicinity of the output cavity 11,thereby allowing the beam confining solenoid 4 to extend upwards of thetube apparatus adjacent the initial portions of the collector 2.Carrying the confining solenoid 4 up to and around the collector regionminimizes beam interception in the output cavity and collector entrancewhereby unwanted secondary emission in this vicinity is kept to aminimum.

A novel output window assembly'is shown in Figs. 1, 2 and 3 whichcomprises the disk-shaped output window 18, as of alumina ceramic,sealed to an annular flanged window cup 19. The flanged portion of thewindow cup 19 is fixedly held by an 'apertured window frame member 21.The window frame member 21 is secured transversely in the outputwaveguide 16. The flanged window cup 19 has a plurality of indentationsor dimples P equally spaced around its perimeter. The indentations.extend inwardly a distance of approximately 0.003" and make physicalcontact with the metalized edge of the ceramic window 18 thus providinga 0.003 gap between the metalized ceramic and the window cup 19. Asolder alloy 20 such as, for example, copper-gold is disposed betweenthe ceramic window and the window cup and alloys with the metallizedceramic and the window cup 19 thereby forming a vacuum-tight ductileseal. The window cup member 19 is made relatively thin, for example,approximately 0.020". The cup is made thin to prevent undue stress onthe ceramic-to-solder-to-cup seal caused by differential coefficients ofthermal ex pansion of the ceramic, solder and cup members.

The window cup 19 may be made of a ductile material as, of, for example,copper or it may be made of a coptrolled because the forces exerted onthe adjacent bonds between the joined elements vary as the mass of thejoined materials. For example, in the ceramic-to-cup joint ias shown inFig. 3, if the thickness of the solder 20 is allowed to become toothick, for example, in excess of 0.005," the force exerted as thetemperature rises, in use, may cause a failure of the ceramic or afailure in the solder-to-ecramic or solder-to-cup bond. The inden-.tations P have been provided to assure proper centering of the ceramicwindow 13 within the window cup 19 thereby controlling the solderthickness and preventing uneven solder thicknesses about the peripheryof the ceramic window 18.

The output waveguide 16 (Fig. 1) has been offset outwardly of the outputwindow 18. It has been found that power reflections from the windowassembly are substantially eliminated over a broad band of frequenciesby providing a certain amount of offset between the axial center linesof the segments of waveguide abutting the window assembly and the centerof the circular window. In the present tube apparatus it has been foundthat an ofiset of approximately 0.325" substantially eliminates powerreflections over the frequency range of the tube. However, the amount ofofiset required for different tubes will vary. The dimensions given hereare to be considered only exemplary and not in a limiting sense.

In addition it has been found that power reflections from the windowassembly may be further reduced by adjusting the geometric center of thedielectric window such that it is slightly radially displaced from theaxial center line of the adjoining segment of waveguide 16 on the tubeside of the window 18.

Referring now to Figs. 1 and 5 there is depicted a novel cathodetake-apart joint 22 comprising a first hollow modified frusto conicalmember 23 held at its large diameter by the end of a hollow cylindricalcathode envelope segment 24. The other or narrow diameter end of thefirst conical member 23 abuts a cathode pole piece 25 therebyestablishing the longitudinal positioning of the cathode assembly l. Asecond hollow modified frusto conical member 26 is secured to the outerwall of the first conical member 23 at its small diameter portion andextends downward and is spaced from said first conical member 23 at itslarger diameter portion. A third modified fnlsto conical member 27 issecured at its narrow diameter to the cathode pole piece 25 and ex tendsdown around the second conical member 26. A portion of the insidesurface of the third conical member 27 abuts a portion of the outsidesurface of the second conical member 26. These abutting surfaces providea transverse cathode aligning interface and aresecured together in avacuum-tight manner as, for example, by a running weld at theiroverlapping ends.

This novel take-apart joint provides an easy means for achievingtransverse and longitudinal alignment of the cathode assembly. 'I'hecathode assembly may be removed by turning the weld oif in a lathe. Inreassembling the tube the cathode need only be assembled and thenrewelded. The proper alignment is retained.

The cavity resonators 7, 8 and 9 have novel tuner assemblies ofsimilar-design associated therewith the tuner assembly of cavityresonator '7 being shown in detail in Fig. 5. A tuning plunger 28 of agood heat and electrical conductive material as of, for example, cop perand having an axial bore therein protrudes into the input cavityresonator 7. A capacitive plunger shield 29 is fixedly mounted to a flatend wall 31 of the cavity resonator and surrounds the inner end of themovable tuning plunger 28, a slot 32 being provided in the capacitiveshield to permit magnetic coupling 'to the space inside the shield 29.

A hollow open-sided cylindrical tuner guide support 33 is secured at oneend to the outside surface of the flat cavity end wall '31 and extendslongitudinally of the tube parallel tothe drift tube 12. A cylindricalplunger 7 guide rod 34 is fixedly secured at one end in the tunerguidesupport 33. A hollow cylindrical plunger bearing 35 as of, forexample, oil impregnated brass is mounted within the plunger bore andslideably bears on the plunger guide rod 34 thereby assuring a'precisely controlled rectilinear travel of the't'uning' plunger 28. Atuner actuating arm 36 is secured to the outer end of the tuning plunger28 and extends substantially perpendicular thereto. A flexible metallicbellows 37 as of, forexample, non-magnetic stainless steel is interposedbetween the actuating arm 36 and the flat cavity end wall 31. Avacuum-tight seal is made at both ends of the bellows 37 where thebellows joins the actuating arm 36 and cavity wall elements whereby avacuum may be maintained within the tube apparatus while allowing fortravel of the tuning plunger 28. r The capacitive shield 29 has beenmade 'concentricall symmetrical with respect to the tuning plunger 28 toprevent the excitation of coaxial electromagnetic modes in the end ofthe plunger surrounded by the bellows 37.

If these coaxial modes are excited the currents induced in 'the plungerand its associated members are likely to requires that the slot 32 liealong a plane substantially parallel to the circumference of theresonator.

The capacitive plunger shield 29 operates such as to minimize thecapacitive effects of the plunger. The resonant frequency of a cavityresonator device is approximately found from the following relationship:

The conductive plunger 28 of the present invention operates upon theinductive portion of the cavity resonator or L in the above formula.However, without the capacitive shield of the present invention,movement of the plunger would also substantially operate upon thecapacitance or C of the above formula. It so happens that without theshield 29 the inductive action of the plunger isoifset by its capacitiveeffect. For example, inward movement of the plunger decreases theinductance L of the the cavity but increases the capacitance C. Byutilizing the novel capacitive shield 29, C remains substantiallyconstant throughout the tuning range of the cavity such that only L is afunction of the plunger travel. It has been found that this novelcombination yields a linear frequency versus plunger travelcharacteristic. The linear tuning characteristic makes this tunerideally suited for use in gang tuners.

The electrical effect of the tuning plunger 28 is to perturb theelectromagnetic field configuration within the cavity resonatorgenerally as shown in Figs. 6 and 6A. When the tuning plunger 28 isfully retracted, as shown in Fig. 6, the amount of magnetic fielddisplacement is a minimum. Fig. 6A shows how the magnetic field is dis-"placed when the tuningplunger 28 is fully extended.

Accompanying the magnetic field displacement is a shift in the strongaxial electric field of the resonator to a point ofl? of its axialcenter line. This means that the electric field in the gap region willbe weaker on the side adjacent the tuning plunger.

It is desirable that substantially the same amount of work be done on anelectron or received from an electron irrespective of its radialposition in the beam. The work done on an electron as it traverses thegap can be found approximately from the relationship where V is the workdone, E is the electric field strength,

a? is an increment of the electron path over which work is being done,and the f is the line inegral over the electron path, From the aboverelationship it can be seen that if E is weaker near the tuning plungerthen, in order for the work V to remain the same, ds must be increasednearer the plunger. Accordingly it will be seen that the gap spacing(integral of ds) has been increased near the tuning plunger by skewingthe end of the drift tube 12.

Hollow tuner actuating rods 38 are secured at one of their ends to theouter ends of actuating arms 36 of the respective tuner assemblies,these rods 38 extending longitudinally of the tube apparatus through aplurality of non-contacting apertures in the flange-like flat cavity end'walls 31 and a collector pole piece 39. The four actuating rods 38 arespaced-apart around the klystron for adequate clearance. A septum 41 islongitudinally disposedin each of the hollow tuner actuating rods 38 andserves to divide the rod into two communicating chamtuner supportbracket 43 is mounted on the collector assembly 2. The tuner actuatingrod extensions 42 pro- 6 trude through annular bearings 43' in the tunersupport bracket 43. i

A Windlass axle 44 is mounted in bearings 44' transversely to thelongitudinal axis of the tuning actuating rods 38 (see Figs. land 7). Aplurality of semi-cylindrical Windlass drums 45 are fixedly mounted onthe Windlass axle 44, separate ones being associated with separate onesof the actuating rods. Channeled Windlass adjustment members 46 (Fig. 1)are pivotally mounted in straddling fashion over a flat chord portion ofeach Windlass drum. A protrusion 46' of each adjustment member engagesan opening in the end of associated band adaptors 47. Band adjustmentscrews 48 are threaded through the adjustment members 46 and theirextremities bear upon an indented portion of the flat side of theassociated Windlass drum 45. Metallic tuning bands 49 are fixedlysecured at one end to the band adaptors 47 and are threaded over thecurved portion of the associated Windlass drums 45. The bands arefurther threaded over rollers 51 with their other ends secured to asecond group of band adaptors 52 which in turn are secured to threadedtuner plugs 53. The threaded tuner plugs 53 screw into threaded holes inone end of the associated tuner actuating rod extensions 42. Locknuts 54screw over the tuner plugs 53 and lock against the end of the actuatingrod extensions 42.

A worm gear 55 is fixedly mounted on the Windlass axle 44 and cooperateswith a tangentially positioned worm shaft 56 to produce rotation of theWindlass drums 45.

In tuning of the cavities, except the output cavity 11, the tuneractuating mechanism operates as follows (see Figs. 5 and 1): Atmosphericpressure serves to provide a force tending to push the tuning plunger 28into the cavity resonator. Restraining this force is the tension in thetuning band 49 which is secured to the Windlass drum 45. Rotationalmotion of the worm gear 55 through the intermediary of the worm shaft 56serves to turn the Windlass drum 45 either permitting the tuning band 49to be drawn by the atmospheric caused force or winding in the tuninghand against the atmospheric caused forces.

Referring now to Fig. 1 it can be seen that the input cavity 7 andintermediate bunching cavities 8 and 9 are mounted with their domedportions facing the cathode assembly 1. However, the output cavityresonator 11 has been reversed such that its tuning plunger 28 entersthe cavity from the cathode end of the tube (Fig. 9). This arrangementreduces the over-all length of the tube apparatus by approximately thelength of a tuning plunger assembly.

Reversion of the output cavity position with respect to the othercavities introduces the complication of having its tuner plunger 28 movein the opposite direction to the other plungers to product the samesense of tuning. In order to obviate this reversed motion requirementthe output cavity Windlass drum 57 was reversed (Figs. 7 and 8). Thetuning band 49 was threaded under instead of over the drum and thenceover the roller 51.

In tuning of the reversed output cavity 11 the tuner actuating mechanismis constructed as follows (see Figs. 7, 8 and 9): A compression spring58 is mounted surrounding the actuating rod extension 42' and bears atits lower extremity upon a' collar 59 fixedly mounted on the actuatingrod extension 42. An apertured header 61 is slideably mounted on theactuating rod extension 42 and bears upon the other end of the spring58. An L- shaped cam lever 62 is pivotably mounted on a pedestal 63. Oneend of the cam lever 62 is forked and bears upon the outward surface ofthe header 61 thereby determining the spring pressure and thus the forceexerted on the tuner actuating rod, said force being counter to theatmospheric force. A cam roller 64 is mounted on the other extremity ofthe cam lever 62. An eccentric cam 65 is axially mounted on the Windlassaxle 44 adja- '7 cent the output cavity Windlass drum'57. The cam rollerrides on the periphery of the cam 65.

In operation of the output ,cavityjtuner the spring tension isdetermined by the position of the lever 62. The initial positioning ofthe cam lever 62 and spring 58 is set such that the spring force justover-balances the atmospheric force thereby taking up the slack in thetuner band 49 and putting some small torsion forces onthe outputWindlass drum 45. When the Windlass is'rotated in a counterclockwisedirection, the cam roller 64 rides over the raised portion of the cam 65and depresses cam lever 62. Depressing the cam lever 62 puts additionalspring force on the tuner actuating rod 38 which then takes up the slackproduced in the tuner band 49. R- tation of the output Windlass drum 57in the clockwise direction causes the spring force to decrease therebymaking it easier for the Windlass to wind in the tuner band 49 againstthe spring force.

In gang tuning of the tube, rotation of Worm shaft 56 imparts rotationto the Windlass axle 44 through the intermediary of Worm gear 55.Adjustment of the individual tuning plungers Within the resonators isprovided by the adjusting screws 48. For example, referring now to 'Fig.the hypothetical frequency versus tuner position characteristics forcavities 7, 8 and 9 are depicted. Cavity 8s characteristic may be movedover to coincide with the characteristic of cavity number 7 by making anadjustment with adjusting screw 48 thereby adjusting the initialpositioning of the tuning plunger.

On the other hand if the tuning rate differs as is shown by curves 7 and9 the previously mentioned adjustment will make the origins of curves 7and 9 coincide but to obtain the same tuning rate (slope) the diameterof cavity number 9s Windlass may be increased.

Thus in summary the present novel tuner assembly, firstly, provides asatisfactory linear tuning characteristic. Secondly, it provides meansfor adjusting the tuning rates of the individual cavities as desired.

A plurality of hollow metallic stringers 67 (Figs. 1 and 4) as of, forexample, non-magnetic stainless steel extend the length of the RF.section to assure rigidity of the tube apparatus. Moreover, certain ofthe stringers 67 convey coolant to the flared initial portion of thedrift tube 12 to prevent overheating. The stringers interconnect theflange-like flat end walls 31 of the cavity resonators and areterminated in the cathode pole piece 25 and collector pole piece 39.

A thin metallic housing 68 covers the Windlass mechanism. -A hollowcylindrical lead shield 69 surrounds the collector assembly and servesas a shield for dangerous X-ray radiation emanating from the collectorin use.

In operation electrons are emitted from the cathode 5, focused into thebeam by the focusing electrode 66 and accelerated through the firstdrift tube 12. The signal to be amplified is fed into the input cavity 7over coaxial line 13 Where the beam is velocity modulated. As themodulated beam travels down the drift tubes 12 it is further modulatedby the intermediate bunching cavities 8 and 9. While Within the drifttube the beam is confined in diameter against forces tending to spreadthe beam, such as space charge forces, by the magnetic field linessupplied by the focusing solenoid 4, said lines of flux being parallelto the drift tube in this region. The output cavity extractselectromagnetic energy from the modulated beam and said energy is thencoupled out of the output cavity through iris 15 and propagated throughwaveguide 16 and Window 18 to the load.

Tuning of the tube is accomplished by the shielded tuning plungers 28and associated tuning apparatus as described above. As above stated,rotation of the singular worm shaft will simultaneously tune all of thecavity resonators of the novel electron tube apparatus.

Since many changes could be made in the above construction and manyapparentlywidely different embodiments of this invention could be madewithout departing from the scope thereof, it is intended that all mattercontained in the above description or shown in the accompanying drawingsshall be interpreted as illustrative and not me limiting sense. a V IWhat is claimed is: h

1. In an electron tube apparatus including, a plurality of cavityresonators arranged for successive electromagnetic interaction with apencil-like electron beam passable therethrough, coupling means forcoupling electromagnetic energy out of the last cavity resonator, ashallow rectangular Waveguide mounted adjacent the cavity resonator withits longitudinal axis substantially parallel to the longitudinal axis ofthe tube apparatus, a beam confining magnetic solenoid mounted coaxiallyof'the beam and enveloping a portion of said waveguide and last cavityresonator for confining the beam, a collector for collecting the beam,and an impedance transformer having its high admittance end disposedtoward the last cavity resonator whereby a shallow section of waveguidemay be utilized in the collector vicinity permitting proper magneticbeam focusing in this area.

2. In a cavity resonator apparatus, a conductive envelope defining thewalls of a cavity resonator, a conductive plunger movable within saidresonator for varying predominately the inductive parameter of theresonator by displacing time varying magnetic field lines, andconductive shield means disposed adjacent said plunger means for holdingsubstantially fixed the capacitive parameter of said resonator byterminating most of the time varying electric field lines whichotherwise would be terminated on said conductive plunger whereby alinear frequency versus tuning plunger travel characteristic may beachieved.

3. An apparatus as claimed in claim 2 wherein said plunger meanscomprises a conductive translatable rod member disposed in'apredominately inductive portion of the cavity resonator.

4. An apparatus as claimed in claim 3 wherein said shield meanscomprises a conductive shield extending into the cavity resonator insurrounding spatial relationship to said plunger whereby said tuningplungers capacitive effect on the resonant frequency of the resonatormay be substantially reduced.

5. A cavity resonator as claimed in claim, 4 wherein said conductiveshield is apertured such that the magnetic lines of force within thecavity resonator may thread through certain volumes of the shieldwherein said plunger is translatable.

6. Acavity resonator as claimed in claim 5 wherein said conductiveshield is concentrically symmetrical with respect to said tuning plungerwhereby electromagnetic coaxial mode excitation in said tuning plungeris substantially eliminated.

7. A cavity'resonator as claimed in claim 6 wherein the cavity resonatorapparatus includes a re-entrant portion, said tuning plunger beingtranslatable within the cavity resonator parallel to the longitudinalaxis of said re-entrant portion, said cavity shield'at its innermost eX-tremity being dome shaped, and a cavity end Wall transverse to andopposite to the innermost extremity of said shield being dome-shapedwhereby the non-tunable in- .ductive portion of the cavity resonator maybe minirnized.

' 8. An apparatus as claimed in claim 3 wherein the cavity resonator isadapted for interaction with'a beam of charged particles and has aninteraction gap space transversely disposed of the beam of particles,the gap spacing increasing transversely of the beam path on the side ofthe cavity adjacent said tuning plunger whereby the interaction betweenthe electromagnetic fields of the cavity resonator and the chargedparticles is substantially the same transversely of the beam.

9. Apparatus as claimed in claim 8 wherein said gap spacing is definedby the spacing between mutually opposing free' end portions ofre-entrant drift tubes.

10. in an apparatus as called for in claim 2 including, an annularmagnetic collector pole piece carried adjacent said collector andextending radially therefrom, said collector pole piece serving toterminate the beam confining magnetic flux lines produced by said beamconfining magnetic solenoid in the collector region, and said collectorpole piece having an aperture therein for passing therethrough saidshallow rectangular Waveguide.

References Cited in the file of this patent UNITED STATES PATENTS2,399,223 Haefl Apr. 30, 1946 2,431,688 'Feenberg Dec. 2, 1947 2,462,856Ginzton Mar. 1, 1949 2,475,646 Spencer July 12, 1949 15 613.806

10 Nordsieck Sept. 26, 1950 Wang Nov. 14, 1950 Litton June 5, 1951 JenksDec. 23, 1952 Edson May 5, 1953 Hansell July 20, 1954 Rich et al Aug.24, 1954 Ginzton Dec. 28, 1954 Clark, Jr. Apr. 12, 1955 Townes Apr. 26,1955 Coyne, Jr., et a1. May 29, 1956 Bennett et a1. Sept. 10, 1957FOREIGN PATENTS Great Britain Dec. 3, 1948 UNITED STATES PATENT oT TcTCE'MHQATE M QURREC'HN Patent No 2 939 036 May 31 1960 Richard o NelsonIt is hereby certified that error appears in the above numbered patentrequiring correction and that the said Letters Patent should read ascorrected below Column 3 line 47 for "OQOOES read 00005 q line 419 forsolder-to eeramie' read older to ceramic column 5 line 50 for "inegrel"read me integral column 8 line 54,, for the claim. reference numeral "6"read me 5 column 9 line l for the claim reference numeral "2" read 1Signed and sealed this 12th day of September 1961,

(SEAL) Attest:

ERNEST W. S DER Commissioner of Patents USCOM M-DC

